Enhanced fretting fatigue strength of TC11 titanium alloy using laser-assisted ultrasonic surface rolling process

Abstract

In this paper, ultrasonic surface rolling (USRP) and laser heating-assisted USRP (Laser-USRP) techniques are employed to enhance the fretting fatigue strength of TC11 titanium alloy. Furthermore, the surface deformation mechanism and fretting fatigue behavior are investigated. The properties of the reinforced surfaces were observed using transmission electron microscope (TEM), microhardness test, residual stress test and fretting fatigue experiments. The results showed that laser-USRP led to a remarkable enhancement in the fretting fatigue life of TC11 titanium alloy compared to traditional USRP. This was mainly due to the fact that laser heating improved the plasticity of TC11 titanium alloy, contributed to the formation of a smoother surface and increased the degree of surface oxidation, which could improve surface lubrication. Under high temperature, more slip systems were activated and more stable dislocations were formed, which resulted in larger compressive residual stress (CRS) with higher stability. The superposition of the elevated temperature field and the kinetic energy of the ultrasonic vibration produced an annealing effect in localized regions, resulting in the formation of more stable gradient nanograins. This study demonstrated the immense potential of laser-assisted plastic deformation in improving the surface properties of titanium alloys.